This invention relates to apparatus for transversely sealing layers of elongated thermoplastic material and, more particularly, to apparatus employing confronting heated platens.
Illustrative of apparatus to which the invention can be advantageously applied is U.S. Pat. No. 4,419,167. There, upper and lower cross bar conveyors are arranged to have parallel runs flanking layers of web material with the means for heating the platens being essentially remote from the path of travel of the web layers. Two problems arise in the utilization of such heated platens. One pertains to the possible scorching of the web material during heat-up of the apparatus and the other relates to the tendency of the web portions between seals to shrink differentially.
We have solved this through a unique, compact and essentially simple apparatus for stretching and/or jogging the web layers while they are in the sealing path. More particularly, the means for stretching and/or jogging includes a vane-equipped shaft operable from the underside of the lower conveyor run in the sealing path. Other objects and advantages of the invention may be seen in the details of the ensuing specification.